Software for reading aloud a text file while displaying it is already commercially available. Such reading aloud software uses a word database (DB) that stores a word and voice information and a syllable DB that stores syllable information. Voice information used herein refers to information obtained by encoding sound of a word pronounced by a human being. Also, a syllable in syllable information refers to the smallest unit of sound that is abstracted so as to form a concrete voice. The syllable information refers to information obtained by encoding sound of a syllable extracted from sound of a word pronounced by a human being. If a word in a sentence to be read aloud is found in such a word database, the afore-mentioned voice information can be used, causing its voice to be naturally audible to a human being. In contrast, if a word in a sentence to be read aloud is not found in the word database, synthetic voice information obtained by combining the afore-mentioned syllable information is used. The synthetic voice information is information obtained by combining syllable information and making adjustments to an accent and an intonation to make it more natural. However, a synthetic voice based on this synthetic voice information sounds unnatural to a human being, as is expected. Related technologies are disclosed by Japanese Laid-open Patent Publication No. 08-87698 and Japanese Laid-open Patent Publication No. 2005-265477.